A device for releasing reactant into the exhaust gas stream of an internal combustion engine is well known from DE 10 2006 049 591 A1. The reactant to be released by this device is a urea solution. In order to mix a urea solution delivered by means of a reactant delivery unit to a reactant injection unit with the exhaust gas stream as efficiently as possible, the reactant delivered in the direction towards the reactant injection unit is heated, for example, to a temperature of about 200° C., in this prior-art device. At the same time, the reactant fed in liquid form into the exhaust gas stream before release is set under such high pressure that an evaporation of reactant before the release of reactant into the exhaust gas stream cannot occur. Such a device utilizes the effect that during the release of reactant into the exhaust gas stream, which reactant is heated and at first under increased pressure, a spontaneous expansion, which leads to a spontaneous evaporation of the reactant, occurs, on the one hand, and, on the other hand, leads to very fine reactant droplets of the portion of the reactant which did not spontaneously evaporate, as a result of which a very efficient and fine mixing of the reactant with the exhaust gas of an internal combustion engine flowing in an exhaust gas duct system is achieved.